Known lane keeping assist devices for a vehicle includes a lane keep assist device including a steering control means operated in accordance with an operation of a steering wheel by a driver for controlling a steering state in accordance with a state of road surface of travel of a vehicle so that the vehicle travels in a lane of travel by controlling the steering state. Further, known lane keeping assist devices for automatically controlling a steering irrespective of an operation by a driver beyond the lane keep assist in order to maintain the vehicle traveling in a lane of travel are disclosed.
For example, JPH2 (1990)-48704A describes an automatic traveling device which sets an optimum target path on a road of travel while searching own path of travel for assisting the vehicle to travel on the target path. In other words, the known automatic traveling device described in JPH2 (1990)-48704A searches a region where the vehicle can travel on its own appropriate target path by recognizing a road edge on the basis of an image of a region in a direction the vehicle traveling in captured by a camera, set appropriate target path within the region where the vehicle can travel, obtains an optimum control target amount in order to merge the vehicle to the target path following a traveling state of the vehicle at that timing, and conduct traveling control of the vehicle in accordance with the control target amount.
JPH2 (1990)-27408A describes a guiding device for vehicle in motion which is constructed to conduct a cornering by calculating a steering amount on the basis of a current direction of the vehicle in motion and an angle of a corner portion using a white line, or the like, provided on a floor for the purpose of showing a limit of a safe path as a guiding line as it is. With the guiding device of the vehicle in motion described in JPH2 (1990)-27408A, a white line drawn on the both sides of a passage in order to indicate a safe path on a floor of plants, or the like, is used as a guiding line, particularly, for the purpose of making cornering operation at narrow space be easy.
JPS60 (1985)-37011 describes an automatic steering device for a vehicle which enables a vehicle to travel without deviating from a forward lane of travel without operation of a steering wheel by a driver. The automatic steering device for a vehicle described in JPS60 (1985)-37011 includes an image capturing means for capturing image of a view of a traveling direction in a bottom right direction of an automobile, a recognizing means for recognizing a line showing a border of a lane of travel from adjacent lane on an image of a road captured by the image capturing means, a distance detection means for detecting distance from a reference position of a line recognized by means of the recognizing means, a steering angle control means for generating a steering angle control signal in accordance with a distance detected by the distance detection means, and a steering angle driving means for changing a direction the vehicle traveling in, in response to a reception of the steering angle control signal from the steering angle control means, for maintaining a distance detected by the distance detection means at a predetermined value by means of an operation of the steering angle control means by the steering angle control signal.
With the constructions described in JPH2 (1990)-48704A, JPH2 (1990)-27408A, and JPS60 (1985)-37011, the traveling on a curve by the vehicle can be conducted along a lane of travel of a vehicle, or the like, which is detected on the basis of images. In this case, it is not always necessary to automatically control the steering irrespective of the operation by a driver, but, for example, cruising operation of the vehicle can be assisted by reducing an operational load of a steering wheel by adding steering torque in order for the vehicle to keep traveling in the center of the lane of travel in response to an operation of the steering wheel by the driver.
With the foregoing known lane keeping assist devices, it is important to detect a lane of travel on a road surface appropriately and safely on the basis of an image captured by a camera. Normally, lane marks for various purposes including lane border lines for recognizing borders between adjacent lanes of travels are drawn on a road surface. Those lane marks include a lane mark with solid line, a lane mark with dotted line, colored lane marks such as in white or in yellow, and colored lane marks with combination of different colors including white and yellow, or the like. The lane marks also include straight lane marks and curved lane marks. It is required to securely detect the lane mark distant from the current position of an own vehicle in order to obtain curvature in order to specify the curved lane mark. Thus, a forward camera which can detect the lane mark distant from the current position of the own vehicle with high precision is required as an image capturing means provided on the lane keeping assist device. Further, although a traveling assist is canceled in case the curvature in the direction the vehicle is traveling in is equal to or greater than a predetermined curvature, a particular measurement is not shown in the known devices despite a cancellation of the traveling assist has to be avoided during a time that the vehicle travels on a road (i.e., curve) having a curved lane mark.
Some vehicles which are recently developed include a forward camera and a rearward camera for watching a view in a forward direction or a view in a backward direction and for parking assist. However, because those known forward camera and rearward camera are only capable for securing images in the vicinity of the vehicle and because the distant images assumes blurred, curvature in the direction the vehicle is traveling in can not be obtained accurately relative to curved lane marks. Thus, the curvature had to be obtained from a traveling locus in the past to be applied, and because a camera which has already been boarded on the vehicle is not converted to detect lane marks and another forward camera with high performance is applied, manufacturing cost of the device is increased.
On the other hand, the device described in JPH2 (1990)-48704A includes a navigation system. Making remarkable progress, recent navigation systems enable to specify current position of a vehicle with high precision using a GPS (i.e., global positioning system) and an inertial navigation. Thus, the information of road configuration in a direction the vehicle traveling in can be detected by the navigation system, and positional coordinates at a predetermined position in the direction the vehicle traveling in can be detected as the information of the road configuration. However, provided that the positional coordinates of the traveling direction of the vehicle is specified using only the detected information from the navigation system, a navigation system with high precision is required because the detection of the positional coordinates is heavily depending on the precision of the navigation system, which increases the manufacturing cost. In addition, in case the forward camera with high precision is required, the manufacturing cost assumes extremely high.
A need thus exists for an inexpensive lane keeping assist device which includes a steering control means for controlling a steering state, a detection means for lane of travel for detecting vehicle's lane of travel on the basis of a captured image for assisting the vehicle to travel within the lane of travel, calculating curvature of a road in the direction the vehicle traveling in on the basis of detected information of a navigation system, calculating curvature of the road along a moving locus of the vehicle on the basis of detected information of the detection means for lane of travel, and assisting traveling of the vehicle on the lane on the basis of curvature of the road in the direction vehicle traveling in estimated by comparing the calculated curvatures.